Poly-4-hydroxybutyrate (PHA4400) is a strong pliable thermoplastic that is produced by a fermentation process, as described in U.S. Pat. No. 6,548,569 to Williams et al. Despite its biosynthetic route, the structure of the polyester is relatively simple:

The polymer belongs to a larger class of materials called polyhydroxyalkanoates (PHAs) that are produced by numerous microorganisms. Steinbüchel, A., Polyhydroxyalkanoic acids, Biomaterials, 123-213 (1991); Steinbüchel A., et al., Diversity of Bacterial Polyhydroxyalkanoic Acids, FEMS Microbial. Lett. 128:219-228 (1995); and Doi, Y., Microbial Polyesters (1990). In nature these polyesters are produced as storage granules inside cells, and serve to regulate energy metabolism. They are also of commercial interest because of their thermoplastic properties, and relative ease of production. Several biosynthetic routes are currently known to produce PHA4400, as shown below:

Chemical synthesis of PHA4400 has been attempted, but it has been impossible to produce the polymer with a sufficiently high molecular weight necessary for most applications (Hori, Y., et al., Polymer 36:4703-4705 (1995)).
Tepha, Inc. (Cambridge, Mass.) produces PHA4400 and related copolymers for medical use, and has filed a Device Master File with the United States Food and Drug Administration (FDA) for PHA4400. Related copolymers include 4-hydroxybutyrate copolymerized with 3-hydroxybutyrate or glycolic acid, as described in U.S. Pat. No. 6,316,262 to Huisman et al., and U.S. Pat. No. 6,323,010 to Skraly et al. Tepha, Inc. has also filed a Device Master File with the United States FDA for copolymers containing 3-hydroxybutyrate and 4-hydroxybutyrate. Methods to control the molecular weight of PHA polymers have been disclosed in U.S. Pat. No. 5,811,272 to Snell et al., and methods to purify PHA polymers for medical use have been disclosed in U.S. Pat. No. 6,245,537 to Williams et al. PHAs with degradation rates in vivo of less than one year have been disclosed in U.S. Pat. No. 6,548,569 to Williams et al. and WO 99/32536 by Martin et al. The use of PHAs as tissue engineering scaffolds has also been disclosed in U.S. Pat. No. 6,514,515 to Williams, and other applications of PHAs have been reviewed in Williams, S. F., et al., Polyesters, III, 4:91-127 (2002).
In the practice of surgery there currently exists a need for absorbable fibers and surgical meshes with improved performance. For example, an absorbable hernia mesh with prolonged strength retention could have many advantages over the non-absorbable synthetic meshes currently used in hernia operations (Klinge, U., et al., Biomaterials 22:1415-1424 (2001)). Long-term implantation of these non-absorbable meshes is not considered ideal because they can lead to complications such as adhesions (fistula formation), pain, and restriction of physical capabilities (Klinge et al., 2001). If implanted into surgical sites that are contaminated or have the potential to become contaminated, 50-90% of these non-absorbable implants will need to be removed (Dayton et al., Arch Surg. 121:954-960 (1986)). These implants are also not ideal for use in pediatric patients where they could hinder growth (Klinge et al., 2001). To date, the use of absorbable synthetic surgical meshes in hernia repair has been found to almost invariably result in large incisional hernias that require revision operations because of the relatively short-term strength retention of these materials (Klinge et al., 2001). However, an absorbable hernia mesh with prolonged strength retention could solve this problem by providing a mechanically stable closure, which can reduce the incidence of adhesions and the risks of infection, and is suitable for use in pediatric patients.
There are also needs for improved meshes and patches for other procedures. In pericardial repair there exists a need for a surgical material that will prevent adhesions between the sternum and heart following open-heart surgery. There are also similar needs to prevent adhesions in spinal and gynecology procedures that could be addressed with improved surgical meshes and patches.
Biomaterial patches derived from animal and human tissue are currently used in cosmetic surgery, cardiovascular surgery, general surgery (including hernia repair), and in urology and gynecology procedures for the treatment of conditions that include vaginal prolapse and urinary incontinence. There is a growing concern about the use of animal and human derived biomaterials because of the risks associated with disease transmission. However, the synthetic absorbable meshes and patches that are currently available are limited, can be inflammatory, and do not provide prolonged strength retention. Thus there exists a need to provide new absorbable meshes for these procedures as well. Ideally, these products should have prolonged strength retention, induce minimal inflammatory responses that resolve, have good handling properties, provide mechanically stable reinforcement or closure, offer anti-adhesion properties (where necessary), minimize the risks of disease transmission, and after absorption leave a healthy natural tissue structure.
Thus, there is a need to develop absorbable fibers with prolonged strength retention that could be used as suturing materials or as surgical meshes.
In 1984, a division of Johnson and Johnson (Ethicon) first introduced a monofilament synthetic absorbable suture made from polydioxanone (sold as PDS™). This suture retains about 50% of its strength up to six weeks after implantation, and is completely absorbed in the body within six months. Davis and Geck subsequently introduced a monofilament suture based on a copolymer of glycolide and trimethylene carbonate (sold as Maxon™). This suture has similar strength retention to PDS™. Two other monofilament sutures were introduced more recently: one based on segmented copolymers of glycolide and caprolactone (sold as Monocryl™), and the other based on a terpolymer of glycolide, p-dioxanone, and trimethylene carbonate (sold as Biosyn™). Monocryl™ is reported to have a 20-30% breaking strength after 2-3 weeks, and is completely absorbed after 3-4 months. Biosyn™ has an absorption profile similar to Monocryl™. Despite continued innovation in the development of absorbable synthetic monofilament sutures there is still a need for a synthetic absorbable suture with extended strength retention for patients requiring long-term wound support. For example, a monofilament suture with 50% strength retention at 3-6 months (after implantation). There are also limited options for synthetic absorbable meshes with prolonged strength retention.
U.S. Pat. No. 6,548,569 to Williams et al. discloses that PHA4400 has a slower absorption rate in vivo than many materials used as absorbable sutures, and provides absorption data for unoriented PHA4400 films and porous samples. Methods to produce medical fibers and textiles from PHA4400 have previously been described by Martin et al. in WO 2004/101002. These methods were successful in producing fibers with prolonged strength retention. WO 2004/101002 discloses poly-4-hydroxybutyrate polymer that can be converted into fibers and devices with tensile strengths comparable to existing absorbable synthetic fibers such as PDS but with prolonged in vivo strength retention. It does not, however, disclose pliable, curl free fibers with increased tensile and knot tying properties as compared to currently available absorbable fibers such as PDS nor methods to produce these important properties.
It is therefore an object of this invention to provide new fibers, surgical meshes, and medical devices with improved handling properties and improved knot tying properties.
It is another object of this invention to provide methods for fabricating the articles and devices.